Thermal transfer systems have been developed to obtain prints from pictures that have been generated electronically, for example, from a color video camera or digital camera. An electronic picture can be subjected to color separation by color filters. The respective color-separated images can be converted into electrical signals. These signals can be operated on to produce cyan, magenta, and yellow electrical signals. These signals can be transmitted to a thermal printer. To obtain a print, a black, cyan, magenta, or yellow dye-donor layer, for example, can be placed face-to-face with a dye image-receiving layer of a receiver element to form a print assembly which can be inserted between a thermal print head and a platen roller. A thermal print head can be used to apply heat from the back of the dye-donor sheet. The thermal print head can be heated up sequentially in response to the black, cyan, magenta, or yellow signals. The process can be repeated as needed to print all colors. A color hard copy corresponding to the original picture can be obtained. Further details of this process and an apparatus for carrying it out are contained in U.S. Pat. No. 4,621,271 to Brownstein.
To promote adhesion of the dye-donor layer to a substrate, an adhesion layer, called a subbing layer, can be used. The subbing layer can be polymeric, as known in the art, and can include an organic titanate or zirconate. Examples of such subbing layers are set forth in U.S. Pat. Nos. 4,929,592 and 4,737,486.
The subbing layer composition used with any specific substrate and dye-donor layer combination can provide various desirable characteristics. For example, the characteristics can include one or more of providing adhesion between the substrate and dye-donor layer, being easily coatable, having good stability over time, and not impacting, or impacting favorably, the resultant colors of the dye-donor patches upon transfer to a receiver.
It is known that organic titanates or zirconates form highly reactive and volatile compositions of low viscosity, making coating difficult. Further, organic titanates or zirconates are known to undergo hydrolysis to form an inorganic polymer of high molecular weight, and an alcohol byproduct. This results in a formulation that is extremely reactive with water, which can be undesirable in a recirculating coating situation. Further, the organic titanate formulations known in the art can readily accept dye, thereby reducing the amount of dye in the dye-donor layer for transfer. See, for example, U.S. Pat. No. 4,933,315.
One method of addressing the above problems in forming a layer including organic titanates or zirconates is to form a shroud of inert atmosphere in the coating area, and control the rate of reaction within the shrouded area. For example, this process is described in co-pending application U.S. Ser. No. 10/765,555 filed Jan. 27, 2004 by Ruschak et al. This requires additional equipment, process controls, and materials, increasing costs. Further, the process is prone to failure if processing conditions are not strictly controlled, and can lead to other defects in the product.
It would be desirable to provide a subbing layer for dye-donor elements used in thermal dye transfer which would provide superior adhesion between a polymeric support and a dye layer comprising a dye dispersed in a binder. It is further desirable to formulate a subbing layer coating composition including metal oxides precursors, wherein the subbing layer coating composition has controlled reactivity with water, good stability over time, and good coatability, and the dry composition has good stability over time, good adhesion properties, and has little or a favorable impact on dye characteristics of a dye-donor layer. It is also desirable to formulate a coating composition and method for forming a metal oxide coating that does not require additional equipment and reduces waste.